Preparation of bagasse and like fibers



United States Patent O 3,302,246 PREPARATION F BAGASSE AND LIKE FIBERS Jose A. Rionda, Thibodeaux, La., assignor to National Bagasse Products Corporation, Vacherie, La., a corporation of Delaware Filed Jan. 16, 1964, Ser. No. 338,232 14 Claims. (Cl. 19-5) This invention relates to the preparation of bagasse and other organic fibers for use in industrial processes as raw material particularly for the manufacture of boards and like structural members commonly termed fiber-board, particle-board, hard-board and the like.

Bagasse is a milled fibrous residue, a by-product of a sugar cane mill, and consists primarily of the crushed stalks of sugar cane from which the juice has been extracted. The bagasse as received from the sugar cane mill generally is composed of the vegetable fibrous stalks and non-fibrous impurities.

The fibrous component of the bagasse includes the rind and the fibro-vascular bundles of the stalk and encompasses the juice-cells which have walls bound and united with pith, a non-fibrous cellulosic substance with the botanical name of parenchyma. Although some pith will generally be found in the bagasse in a loose form, the major part of the pith is bonded to and inside the fibers, so as to form the latter into small bundles. In addition to the fiber and pith, bagasse also contains small amounts of sugar, sugar polymers, gums, waxes, dirt, leaves and other impurities.

The production of a uniform grade of industrially acceptable, clean, high quality bagasse fiber is extremely difficult. Not only must the individual fibers be properly sized, but they must be separated from and cleansed of the dirt, pith and other impurities adhered thereto and/ or admixed therewith. The loose pith is, of course, fairly easy to separate, but much more difficult is that which binds the fibers into bundles, since these bundles must be opened before the removal of the pith can be effected. In order to enable the bagasse and other similar vegetable fibers to compete successfully as a source of raw material, therefore, it is necessary to obtain economical and efiicient processes of and means for removing pith, dirt and other impurities without weakening the fiber strength.

Heretofore, most processes for cleaning and depithing bagasse have been designated as either wet or dry.

Wet processes usually consist of subjecting bagasse, in the form of a suspension or slurry having from about 1 to 9% solids, to screening and refining, and if pulp is desired, to cooking and digesting with chemicals and at high temperatures. amounts of power and a high capital investment per ton of production. Yields usually are low and in the neighborhood of 35 to 55% of usable fiber based on the total starting quantity of bagasse. Thus, while the quality of the finished ber can be of the best, total cost of production can be prohibitively high.

Dry processes are usually characterized by their relative simplicity and low initial costs, and usually involve the use of some sort of screening to separate fine from Such a wet process requires large coarse particles, and the use of rod or hammer mills or 3,302,246- Patented Feb. 7, 1967 TCC of about 49 to 53%. By way of definition in this art, bagasse having a moisture content less than the aforesaid range is termed dry bagasse, while bagasse having a moisture content higher than the said range is termed wet bagasse. In any given batch, of course, the actual moisture content will be the resultant of the influence of such factors as ambient temperature and humidity, externally applied or internally developed heat, amount of moisture added, etc., on the starting moisture content of the raw bagasse.

In one particular type of dry process the use of which has heretofore been proposed, the raw bagasse is baled, stacked, and covered in such a manner that a subsequent natural fermentation at temperatures of under F. is obtained. This natural fermentation, initiated by wild bacteria and yeast cells either present in the bagasse or air-borne to the stacks, produces alcohol and then acetic acid, utilizing as nutrients the sugars, waxes and gums present in the raw bagasse. During the natural fermentation the acidity of the bagasse undergoes a marked increase, which aids the loosening of the pith, while consuming most of the sucrose, glucose, fructose and other non-fibrous organic impurities. The rise in temperature produced by the natural fermentation partially evaporates the moisture in the bagasse, reducing it from its initial level of approximately 50% to the range of about 13 to 30%. Subsequent oxidation and evaporation eliminate the acetic acid produced by the fermentation, thus decreasing the acidity to nearly neutral. Thereafter, the bales are broken up into chunks, moisture is added to effect an appreciable rise in the moisture content of the raw bagasse, at times to a point sufficiently high to make the bagasse wet, and the resultant swelled fibers and pith are then subjected sequentially to a milling operation, a classifying operation, and another milling operation, all intended to remove as much pith as possible, preparatory to a drying of the final bagasse fibers so as to ready them for use in the desired subsequent manufacturing operations.

This process has, however, failed to gain any substantial commercial acceptance by virtue of the fact that it has not proved to be feasible therewith to achieve both the desired optimum separation of the fibers from thepith and the desired maximum yield of the best quality fiber.

It is an important object of the present invention, therefore, to provide novel and improved methods of and means for treating and processing bagasse and other vegetable brous materials so as to obtain a maximum yield of high quality depithed and decorticated fiber of optimum length and strength characteristics at a minimum cost.

Another object of the present invention is the provision of highly efficacious methods of and means for separating pith and other impurities from bagasse and other vegetable fibrous materials through specialized classifying and milling operations carried out in alternating sequence.

The foregoing and other objects, characteristics and advantages of the present invention will be more clearly understood from the following detailed description thereof when read in conjunction with the accompanying drawing, in which:

FIG. l is a schematic illustration, in the format of a flow diagram, of a plant or system for processing bagasse in accordance with one aspect of the present invention; and

FIG. 2 is a similar illustration of such a plant or system in accordance with a somewhat modified aspect of the present invention. l

It is to be understood that the principles of the present invention, although described herein in connection with the processing of bagasse (fermented or otherwise), are also applicable to other mature stalk materials of a fibrous nature, such as bamboo, sorghum, corn stalks, broom straw, flax, hemp, etc.

Referring now to the drawing in greater detail, and in particular to FIG. l, in accordance with one aspect of the present invention the dry raw bagasse having a moisture content of between about 13 to 30% based on its own weight, preferably in baled form and following a suitable fermentation period, is fed, as indicated at 1, into a bale breaker 2 in which the bales are broken up into relatively small chunks or fiat bundles of fibers, commonly termed shives, each about 4 inches long, about 1/2 inch wide and about 1A inch thick. In each such shive, the various bers are generally held together by pith. The bale breaker 2, for example a hammer mill, is of slightly modified construction, operating under a slight suction, draft or negative pressure which facilitates the disintegration of the bales and a simultaneous partial separation of the pith and dirt from the bagasse. By virtue of this construction, the light fraction of the disintegrated baled material, which amounts to about 2% of the total starting mass fed into the bale breaker Iand includes loose pith, dirt, sand, etc., and all particles less than 1/8 inch in the largest dimension and having a relatively large area to mass ratio, is extracted from the bale breaker at 3 and is conducted away to a location and for a purpose to be more fully explained, presently.

The heavy fraction of the disintegrated, baled, fibrous material which remains and consists principally of the aforesaid shives, is now fed, as indicated at 4, to a first air-classifier 5 where it is separated into two fractions. The light fraction, containing pith, sand, dirt and small degraded fibers less than 3/16 inch long, and which amounts to about 5 to 10% of the incoming feed, is taken off at 6 and joined with the light fraction from the bale breaker or hammer-mill 2, and its processing will be more fully set forth hereinafter. The heavy fraction, amounting to about 90 to 95% of the incoming feed and as previously indicated principally composed of shives, is taken off at 7 and fed to an attrition mill 8, preferably of the rotary disc type well known in the art, or alternatively to a rod, cage or wing beater or refiner, depending on the type and size of fiber desired. In the case of an attrition mill, the discs will generally be spaced between 'about 0.030 and 0.090 inch apart.

The fibrous mass leaving the attrition mill 8 at 9 consists of shives to the extent of about 15 with the remainder composed of loose fibers as well as pith, leaves, dirt, etc., the fibers ranging in length up to about 11/2 inches. This mass is then fed into a second two-fraction air-classifier or separator 10. The light fraction, which amounts to about 15% 0f the incoming feed, is taken off at 11 and consists essentially of pitch, dirt, etc. and fibers ranging in length up to about 5)/16 inch, and its further processing will be described more fully hereinafter.

The heavy fraction leaving the separator or classifier at 12 is fed into a second rotary disc-type attrition mill 13 or the like device which is set, for example, at a disc spacing of between about 0.005 and 0.040 inch. The resulting fibrous mass leaving the mill at 14 is composed principally of fibers having an average length of between about `1/2 and 1% inch, with a maximum length of about 1% inches, and of a relatively small amount (less than about 3%) of shives. In order 4to facilitate the second milling operation, however, it is found desirable to carry the same out with the fibers somewhat more flexible and soft 'and thus somewhat less brittle than the fibrous mass subject to the first milling operation. As will be readily understood, the various preceding classifying and milling operations, as well as the air feed of the fibers from each stage to the next, all result in certain reductions in moisture content, so that the natural moisture content of the bagasse may not suffice to provide the desired softness and flexibility of the fibers. Thus,

with the raw baled bagasse, having a moisture content of about 18% based on its own weight, the heavy fraction taken off the separator 10 may have a moisture content of only about 11% based on its own weight.

To avoid this potential drawback, water may be yadded to the heavy fraction extracted from the second classifier or separator 10 at the inlet to the attrition mill 13, as indicated at 15, in order to enable the moisture content of the incoming feed to be supplemented to the required extent. For the implementation of the principles of the present invention, it is found acceptable if the moisture addition at 15 is sufficient to impart to the mass leaving the second attrition mill 13, taking into account the reduction in moisture content occurring normally during this milling operation, a moisture content of about 25 to 30%v based on the weight of this mass.

If desired, specified chemicals may first be added to the water to form a solution that will concurrently adjust the acid content of the mass to any predetermined value. The water or chemical solution may be sprayed onto the fibrous mass either separately or as an adjunct of the infeeding thereof to 4the second milling operation in the attrition mill 13. At the same time, this water addition stage may be employed to introduce fire retardant compositions to the fibrous mass.

The second milling operation thus may be effected much more thoroughly, with finer milling and with smaller clearances, and yet without damage to the fibers, than would be possible with a dry-milling operation. This is due to both the prior separation of those fiber particles already of adequate size, and the softening and making more fiexible of those that pass through the second mill. Furthermore, raising of the moisture content of the fiber mass at this stage of the processing, rather than prior to the first milling operation, has the advantage that the mass contains less pith to which the water can be attracted (pith normally being about three times as hygroscopic as the bagasse fibers), and that with the fibers already substantially separated, such pith as still is present is incapable, despite the influx of water, of again bonding the fibers to one another.

The so-prepared fibrous mass is now brought to the desired low moisture content of about 11/2 to 5% based on its own we-ight by being fed through a dryer 16 from which it is passed to a third two-fraction classifier or separator 17. In the latter, most of the remaining pith and dust, amounting to about 5% of the incoming feed, is removed as the light fraction, as indicated at 18. The heavy fraction leaving the third classifier 17 at 19 and amounting to about of the total mass coming from the dryer, is the finished processed fiber except as hereinafter indicated.

The light fractions extracted at 3, 6, 11 and 18 from the bale breaker 2 and theclassifiers 5, 10 and 17, respectively, are blended together at 20 and fed to a fourth two-fraction classifier or separator 21. The light fraction extracted from this classifier is taken off at 22 and disposed as waste, being principally dust and very short fibers, and may be used as boiler fuel or as a filler for molded products. The heavy fraction from the fourth classifier 21 is reclaimed fiber and is taken off at 23 and blended back into the feed going to the dryer 16, thereby further enhancing the economies of the entire processing by reducing waste of usable fibers to a minimum.

The heavy fraction extracted from the third classifier 17 thus is seen to be composed of the basically extracted fibers and of a portion of the reclaimed fibers obtained by recycling the various light fractions through the fourth classifier or separator 21. The finished processed fiber is found to be an extremely high grade fiber, therefore, with a minimum amount of pith content (ranging up to about 7%) and degree of ber degradation, which in every way is superior to a corresponding fiber produced by conventional dry processes. The finished fiber is, consequently, extremely well suited for use in the manufacture of fiber-board and other industrial products requiring individualized fibers of substantial length and strength and a great degree of freedom from pith. The preparation of the fiber according to the present invention is also characterized by the fact that energy, power, and capital investment `costs are far lower than those for a wet process.

`The processing of the bagasse in accordance with the aspect of theinvention illustrated in FIG. 2 differs from that of FIG. 1 in the use of a pair of three-fraction classifiers or separators 5 and 10 in lieu of the two-fraction classifiers 5 and 10, respectively, for the first and second classification stages. The middle fractions, composed of generally intermediate size particles, e.g. fibers up to about 3%; inch long, are taken off the respective classifiers at 5l and 10 and are bypassed around the associated attrition mills 8 and 13. The middleI fraction from the first classifier 5' is blended with the output of the mill 8 being fed into the second classifier 14V, and the middle fraction from the latter is blended with the output of the mill 13 being fed into the dryer 16. This last blend will thus have a considerably lower average moisture content than the mass leaving the second mill 13 and will, consequently, be more easy to handle, both mechanically and pneumatically. In general, the middle and heavy fractions taken off at 5 and 7 will comprise about 15% and about 75 to 80%, respectively, of the total output of the first classifier 5', While the middle and heavy fractions taken off at 10 and 12 will comprise about 40% and about 45%, respectively, of the total output of the second classifier 10.

Since in all other respects the methods of fiber processing and preparation according to FIGS. 1 and 2 are substantially identical, a detailed description of the FIG. 2 method is deemed unnecessary and will not be undertaken herein. As will be readily recognized, however, the present invention in any of its forms provides novel methods of and means for dry processing dry bagasse which, by reason of the herein described elimination of disadvantageous aspects of known methods and means of processing bagasse, renders possible the production of a high grade bagasse fiber suited for the manufacture of industrial products having a high degree of commercial acceptability heretofore not attainable by products made from conventionally processed bagasse fiber.

It should be noted that the raw bagasse or other fibrous material need not be baled for the purposes of the present invention. If such raw fibrous material is at hand in bulk, therefore, and unbaled, it may be fed directly into the first classifier 5 or 5', as indicated in phantom at 24 in FIGS. l and 2, enabling the bale-breaking step to be omitted entirely.

Although there have been described herein preferred aspects of the fiber-processing methods and means according to the present invention, it is to be understood that the foregoing disclosure is for purposes of illustration only, and that the various features, proportions and relationships set forth may be modified and varied in a number of ways none of which involves a departure from the spirit and scope of the present invention.

I claim:

1. The method of processing bagasse and like vegetable fibrous materials, comprising the steps of subjecting raw dry bagasse to a first classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, subjecting the remaining heavy fraction composed :principally of shives to a first milling operation to break up at least a major portion of the shives into loose fibers while separating pith therefrom, subjecting the so-formed mass to a second classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, subjecting the remaining heavy fraction composed principally of separated fibers and a minor proportion of shives to a second milling operation to effect further breaking up of shives into loose fibers and separation of pith from fibers, and subjecting the so-formed mass to a third classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, blending all of said light fractions with one another, subjecting the so-formed blend to a fourth classifying operation wherein loose pith, dirt and other impurities as well as other small particles and excessively degraded bers are removed as a light fraction for disposal, and recycling the remaining heavy fraction composed principally of reclaimed usable fibers into admixture with the mass formed by said second milling operation.

2. The method of processing bagasse and like vegetable fibrous materials, comprising the steps of subjecting raw dry bagasse to a rst classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, subjecting the remaining heavy fraction composed principally of shives to a first milling operation to break up at least a major portion of the shives into loose fibers while separating pith therefrom, subjecting the so-formed mass to a second classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, subjecting the remaining heavy fraction composed principally of separated fibers and a minor proportion of shives to a second milling operation to effect further breaking up of shives into loose fibers and separation of pith from fibers, drying the mass formed by said second milling operation to reduce the moisture content of this mass to between about 11/2 and 5% based on its own weight, and subjecting the so-formed mass to a third classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, blending all of said light fractions with one another, subjecting the soformed blend to a fourth classifying operation wherein loose pith, dirt and other impurities as well as other small particles and excessively degraded fibers are removed as a light fraction for disposal, and recycling the remaining heavy fraction composed principally of reclaimed usable fibers into admixture with the mass formed by said second milling operation prior to the drying of this mass.

3. The method of processing begasse and like vegetable fibrous materials, comprising the steps of subjecting raw dry bagasse to a first three-fraction classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, subjecting the heavy fraction provided by the first classifying operation and composed principally of shives to a first milling operation to break up at least a major portion lof the shives into loose fibers while separating pith therefrom, blending the so-formed mass with the middle fraction provided by the first classifying operation and composed of intermediate size particles, subjecting the so-formed blend to a second three-fraction classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, subjecting the heavy fraction provided by the second classifying operation and composed principally of separated fibers and a minor proportion of shives to a second milling operation to effect further breaking up of shives into loose fibers and separation of pith from fibers, blending the so-formed mass with the middle fraction provided by the second classifying operation and composed of intermediate size particles, and subjecting the so-formed blend to a third classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as a light fraction, whereby the remaining heavy fraction comprises the finisher processed fiber.

4. The method of claim 3, further comprising the steps of blending all of said light fractions with one another, subjecting the so-formed blend to a fourth classifying operation wherein loose pith, dirt and other impurities as well as other small particles and excessively degraded fibers are removed as a light fraction for disposal, and recycling the remaining heavy fraction composed principally of reclaimed usable fibers into admixture with the blend formed of the mass provided by the second milling operation and the middle fraction provided by the second classifying operation.

5. The method of claim 3, further comprising the step of drying the blend formed of the mass provided by the second milling operation and the middle fraction provided by the second classifying operation, for reducing the moisture content of this blend to between about 11/2 and 5% based on its own weight.

6. The method of claim 5, further comprising the steps of blending of said light fractions with one another, subjecting the so-formed blend to a fourth classifying operation wherein loose pith, dirt and other impurities as well as other small particles and excessively degraded fibers are removed as a light fraction for disposal, and recycling the remaining heavy fraction composed principally of reclaimed usable bers into admixture with the blend formed of the mass provided by the second milling operation and the middle fraction provided by the second classifying operation prior to the drying of this last-named blend.

7. The method of claim 3, further comprising the steps of adding moisture to the heavy fraction provided by the second classifying operation in amounts sufficient to impart to the mass provided by the second milling operation a moisture content of between about 25 and 30% based on the weight of this mass, and drying the blend formed by this mass and the middle fraction provided by the second classifying operation, for reducing the moisture content of this blend to between about 11/2 and 5% based on its own weight.

8. The method of claim 7, f-urther comprising t-he steps of blending all of said light fractions with one another, subjecting the so-formed blend to a fourth classifying oper-ation wherein loose pith, dirt and other im- =purities as well as other small particles and excessively degraded fibers are removed as a light fraction for disposal, and recycling the remaining heavy fraction composed principally of `reclaimed usable fibers int-o admixture with the blend formed of the mass provided by the second milling operation and the middle fraction provided by the second classifying operation prior to the drying of this last-named blend.

9. The method of claim `8, wherein the raw dry bagasse is initially in the form of bales, further comprising the steps of subjecting said bales to a shredding operation prior to the first classifying operation to disintegrate the bales into a major heavy fraction composed of shives and smaller loose particles lof pith, dirt and other impurities and into a minor light fraction composed principally 4of loose pith, dirt and other small particles less than 1/s inch in their largest dimension and having a relatively large a-rea to mass ratio, extracting the heavy fraction provided by the shredding operation for subjection to the first classifying operation, and blending the light fraction provided by the shredding operation with the light fractions provided by the first, second and third classifying operations.

10. A plant for processing bagasse and like vegetable fibrous materials, comprising first separator means for subjecting raw dry bagasse to a rst classifying operation wherein loose pith, dirt land other impurities as well as other small particles and fibers are removed as a light fraction, first milling means for subjecting the remaining heavy fraction composed principally of shives to a first milling operation to break up at least a major portion of the shives into loose fibers While separating pith therefrom, second separator means for subjecting the soformed mass to a second classifying operation wherein loose pith, dirt and other impurities as well as other small particles and fibers are removed as -a light fraction, second milling means for subjecting the remaining heavy fraction composed principally of separated fibers and a minor proportion of shives to a second milling operation to effect further breaking up of shives into loose fibers and separation of pith from fibers, and third separator means for subjecting the so-formed mass to a third classifying operation wherein loose pith, dirt and other impurities as well as other small'particles and fibers are removed as a light fraction, whereby the remaining heavy fraction comprises the finished processed fiber.

11. A plant according to claim 10, further comprising dryer means interposed between said second milling means and said third separator means for drying the mass formed by the second milling operation prior to the third classifying operation.

12. A plant according to claim 10, further comprising means for adding moisture to the heavy fraction provided by the second classifying operation in advance of the sta-rt yof the second milling operation, thereby t-o ensure that the mass yformed by the second milling operation has a lmoisture content of between about 25 to 30% based on its own weight, and dryer means interposed between said second mi'l-ling means and said third separator means for drying the mass formed by the said second milling operation prior to the third classifying operation.

13. A plant according to claim 12, furthe-r comprising fourth separator means, means for feeding a blend of the light fractions provided by said first, second and third separator means into s-aid fourth separator means, means for conduct-ing the light fraction provided by said fourth separator imeans and composed of loose pith, dirt and other impurities as well as other small particles and eX- cessively degraded fibers to a waste disposal station, and means for conducting the heavy fraction provided by said fourth separator means to the entry of sai-d dryer means for admixture with the mass formed by the second milling operation.

14. A plant according to claim 12 said first and second separator means each being constructed to provide an additional middle fraction composed of intermediate size particles, means for bypassing the middle fraction provided by said first separator means around sai-d first milling means for admixture with the mass provided by the first milling operation prior to the second classifying operation, and means for bypassing the middle fraction provided by said second separat-or means around said second milling means for admixture with the moisturized mass provided by the second milling operation prior to the entry of this mass into said dryer means.

References Cited by the Examiner UNITED STATES PATENTS 2,452,533 10/1948 Wells 19-5 MERVIN STEIN, Primary Examiner.

D. NEWTON, P. C. FAW, Assistant Examiners, 

1. THE METHOD OF PROCESSING BAGASSE AND LIKE VEGETABLE FIBROUS AMTERIALS, COMPRISING THE STEPS OF SUBJECTING RAW DRY BAGASSE TO A FIRST CLASSIFYING OPERATION WHEREIN LOOSE PITH, DIRT AND OTHER IMPURITIES AS WELL AS OTHER SMALL PARTICLES AND FIBERS ARE REMOVED AS A LIGHT FRACTION, SUBJECTING THE REMAINING HEAVY FRACTION COMPOSED PRINCIPALLY OF SHIVES TO A FIRST MILLING OPERATION TO BREAK UP AT LEAST A MAJOR PORTION OF THE SHIVES INTO LOOSE FIBERS WHILE SEPARATING PITH THEREFROM, SUBJECTING THE SO-FORMED MASS TO A SECOND CLASSIFYING OPERATION WHEREIN LOOSE PITH, DIRT AND OTHER IMPURITIES AS WELL AS OTHER SMALL PARTICLES AND FIBERS ARE REMOVED AS A LIGHT FRACTION, SUBJECTING THE REMAINING HEAVY FRACTION COMPOSED PRINCIPALLY OF SEPARATED FIBERS AND A MINOR PROPORTION OF SHIVES TO A SECOND MILLING OPERATION TO EFFECT FURTHER BREAKING UP OF SHIVES INTO LOOSE FIBERS AND SEPARATION OF PITH FROM FIBERS, AND SUBJECTING THE SO-FORMED MASS TO A THIRD CLASSIFYING OPERATION WHEREIN LOOSE PITH, DIRT AND OTHER IMPURITIES AS WELL AS OTHER SMALL PARTICLES AND FIBERS ARE REMOVED AS A LIGHT FRACTION, BLENDING ALL OF SAID LIGHT FRACTIONS WITH ONE ANOTHER, SUBJECTING THE SO-FORMED BLEND TO A FOURTH CLASSIFYING OPERATION WHEREIN LOOSE PITH, DIRT AND OTHER IMPURITIES AS WELL AS OTHER SMALL PARTICLES AND EXCESSIVELY DEGRADED FIBERS ARE REMOVED AS A LIGHT FRACTION FOR DISPOSAL, AND RECYLCING THE REMAINING HEAVY FRACTION COMPOSED PRINCIPALLY OF RECLAIMED USABLE FIBERS INTO ADMIXTURE WITH THE MASS FORMED BY SAID SECOND MILLING OPERATION. 